Automatic reference-pressure balance method

ABSTRACT

The present invention provides a system and method for calibrating pressure sensors associated with chambers in a processing facility. The system calibrates the pressure sensors while the chamber are open to each other, such as through an open slit valve or vacuum sealed door. Maintaining the pressure in the chambers relative to each other prevents a rush of gases, condensate or other foreign materials into an adjacent chamber that may occur when the pressure between the chambers is not equalized. This prevents contamination of the materials being processed, and eliminates the need for system shutdown to calibrate sensors. Also, since calibration occurs every time the slit valve is open, the calibration is real-time and does not allow the pressure differential between the chambers to become too great.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation in part of patent applicationSer. No. 09/137,354, filed Aug. 20, 1998 which claims priority from U.S.

[0002] Provisional Patent Application Ser. No. 60/056,821, filed Aug.22, 1997.

TECHNICAL FIELD

[0003] This invention relates generally to semiconductor processing and,more particularly, to a system and method for calibrating gas or liquidpressure during wafer processing.

BACKGROUND

[0004] Contamination of materials is a factor in many manufacturingprocesses, and is of particular concern in the fabrication of integratedcircuits.

[0005] In general, integrated circuit technology is based on the abilityto form numerous transistor structures on a single semiconductorsubstrate. Typically, multiple integrated circuits will be formed on asingle silicon wafer, the wafer providing the semiconductor substratefor the circuits. The intricacy of the circuits and the large number ofsteps involved in the fabrication make it essential that each of theprocess steps be tightly controlled and meet very stringentspecifications to prevent any type of contamination. To increase thepurity and hence the quality and reliability of manufacturing processes,most are done in sealed rooms or chambers, where the environment,including temperature, pressure and purity of liquids or gasesintroduced can be controlled. One of the biggest sources ofcontamination occurs when the product being manufactured is transferredfrom one area of the manufacturing process to the next, whichnecessitates opening a door or valve to introduce the material into thenext chamber or room. When the door or valve is open, if there is apressure differential between the chambers, the potential forcontamination is increased. Processing fluid and/or gas will rush fromthe chamber with the higher pressure to the chamber with the lowerpressure to equalize the pressure, bringing solids and liquids alongwith the gas, which may cause such problems as condensation andparticulate contamination on the material being manufactured.

[0006] The solutions used to mitigate the above-identified problem haveincluded: reducing the amount of time that the door or valve is openedto reduce the amount of contaminants that enter the chamber; making thetransfer in two stages; utilizing an intermediate or transfer chamberinto which only one of the other chambers is opened at a given time;placing calibrated pressure sensors in each chamber; and tying thepressure sensors into the valve-opening mechanisms in both chambers toobtain a desired, consistent pressure balance before the valve betweenthe chambers is opened. However, these solutions, separately or incombination, do not always adequately resolve the aforementionedproblems.

[0007] Even minimizing the time the door or valve is open will result insome contamination, especially if the pressure is not equalized betweenthe two chambers before opening the door or valve. One of the biggestproblems in equalizing the pressure is keeping the pressure sensorscalibrated, as sensors tend to drift in calibration over time. If thepressure sensor in either chamber is out of calibration, the pressurebetween the two chambers will not actually be equal, and when the dooror valve is open, the gas will rush from the higher to lower pressurechamber to equalize the pressure. The effective drift of the pressuresensors is actually doubled if the two sensors drift calibration inopposite directions. If a sensor has drifted, process overseers aregenerally unaware of the problem until a rush of gas between thechambers has occurred, resulting in contamination of a manufacturedproduct. In order to re-calibrate sensors that have drifted, themanufacturing process generally has to be shut down, and the sensortaken off-line to be calibrated, resulting in production down-time.

[0008] U.S. Pat. No. 5,808,175 issued Sep. 15, 1998 to Shen-Yan Changdiscloses a method of temporarily, manually mounting a second, in-linecalibrated sensor to the same chamber for the purpose of monitoring orcorrecting the first sensor. However, Chang only utilizes the secondsensor for comparison to the readings obtained from the first sensor forthe same chamber, to determine if it needs replacing. If there is driftin the sensors used to read the pressure in different chambers, asituation may still occur wherein the pressure differential between twochambers is such that a rush of gas and contaminants occurs when thedoor or valve between the two chambers is opened.

[0009] It would, therefore, be desirable to be able to provide a methodand apparatus wherein the pressure in the two chambers between whichmaterials are being transferred can be kept equal so that there will notbe a rush of gas between the two chambers when the door or valve isopened.

SUMMARY

[0010] The present invention overcomes the above outlined problems and atechnical advance is achieved by a system and method that equalizes andcalibrates the pressure of two or more chambers on either side of avalve (door) during operation. In one embodiment, the method isperformed each time the valve is opened. When the valve is opened, thepressure in the chambers will equalize. After the pressure in thechambers has equalized, pressure readings from sensors mounted in eachchamber are calibrated relative to each other.

[0011] In some embodiments, the pressure readings are sent to a controlmodule. The control module evaluates the readings taken from the sensorsand adjusts them to match each other.

[0012] In some embodiments, there may be an intermediate, or transferchamber between a process chamber and a loading chamber. The sensorreadings from the process and loading chambers are adjusted to match thesensor readings of the transfer chamber. As a result, all the chamberswill be calibrated with the transfer chamber, and therefore with eachother.

[0013] Since calibration occurs every time the valve is open, thepressure differential between the chambers never becomes too great. As aresult, there is little if any fluid flow (e.g., a flow processing gasesand/or contaminants) between the chambers and a very clean chamberenvironment is maintained.

[0014] Also, because the relative calibration is done during actual use,the system does not have to be shut down to perform calibrationroutines. This, of course, results in increased productivity and cycletime.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a diagram of an exemplary processing facility thatutilizes a transfer chamber between operational chambers.

[0016]FIG. 2 is a diagram of an exemplary processing facility that doesnot utilize a transfer chamber between operational chambers.

[0017]FIG. 3 is a method flow diagram showing the steps taken incalibrating the pressure sensors.

[0018]FIG. 4 is a diagram of two chambers of FIG. 1, separated by avalve.

[0019]FIG. 5 is a diagram of the two chambers of FIG. 4 showing thepressure in each chamber being calibrated relative to the other chamberwhile the valve is open.

DETAILED DESCRIPTION

[0020] Referring to FIG. 1, reference numeral 10 designates a portion ofan integrated circuit processing facility including two loading chambers12, 14, a transfer chamber 16, and two process chambers 18, 20. Loadingchambers are typically used for loading and unloading one or morematerials for processing. Processing chambers are typically used forperforming processing operations, and may include additional componentsfor varying the temperature of the chamber or for adding processingfluids and/or constituents into the chamber. Transfer chambers are oftenused as an intermediate chamber between loading chambers and processingchambers, and may include a robot arm or some equivalent device formoving materials between the different chambers. To facilitateprocessing and maintain a clean environment, the different chambers mustbe hermetically sealed from each other at particular times.

[0021] The loading chambers 12, 14 are connected to the transfer chamber16 through slit valves 22, 24, respectively. Likewise, the processchambers 18, 20 are connected to the transfer chamber 16 through slitvalves 26, 28, respectively. Connected to the transfer chamber 16 is anexhaust line 40 with a variable restriction control valve 42 used forcontrolling the pressure in the chamber. Likewise, connected to theloading and process chambers 12, 14, 18, 20 are exhaust lines 44, 46,48, 50 with variable restriction control valves 52, 54, 56, 58,respectively. Each of the variable restriction control valves 42, 52,54, 56, 58 is controlled by a control module 60.

[0022] The control module 60 receives pressure readings from pressuresensors (e.g. transducers) 62, 64, 66, 68, 70 connected to loadingchambers 12 and 14, transfer chamber 16, and process chambers 18, 20,respectively. Furthermore, the control module 60 is informed of thestatus (open or closed) of slit valves 22, 24, 26, and 28 throughmonitor lines 72, 74, 76, 78 respectively.

[0023] In operation, the control module 60 reads the pressure of theloading chamber 12 through the pressure sensor 64 and the transferchamber 16 through the pressure sensor 62. The control module 60 thenequalizes the pressure in the two chambers 16 and 12 by adjusting thevariable restriction control valves 42 and 52 accordingly. As a result,the pressure in the loading chamber 12 matches that of the transferchamber 16. Every time that the slit valve 22 is open between thechambers, the control module 60 calibrates the pressure sensors 62 and64 relative to each other. The same process is performed every time theslit valve 24, 26, or 28 is open between the transfer chamber 16 and theloading or process chamber 14, 18, or 20, respectively. In aconfiguration of the system that utilizes a transfer chamber 16, such asthat shown in FIG. 1, the pressure sensors for the chambers on eitherside of the transfer chamber are calibrated in reference to the pressuresensor for the transfer chamber so that it will be accurate regardlessof which chamber connecting into it is opened at any one time.

[0024] Referring now to FIG. 2, the reference numeral 80 designates aportion of an integrated circuit processing facility with a directchamber-to-chamber connection, including a loading chamber 12, and aprocess chamber 18. In this embodiment, the loading chamber 12 and theprocess chamber 18 are similar to those described in FIG. 1, except thatno intermediate transfer chamber exists there between. The loadingchamber 12 is connected to the process chamber 18 through the valve 22.Connected to the loading chamber 12 is an exhaust line 44 with avariable restriction control valve 52, used for controlling the pressurein the chamber. Likewise, connected to the process chamber 18 is exhaustline 48 with variable restriction control valve 56. Each of the variablerestriction control valves 52, 56 is controlled by a control module 60.

[0025] The control module 60 receives pressure readings from pressuresensors (e.g. transducers) 64, 68 connected to the loading chamber 12and the process chamber 18, respectively. Furthermore, the controlmodule 60 is informed of the status (e.g. open or closed) of the slitvalve 22 through the monitor line 72.

[0026] In operation, the control module 60 reads the pressure of theloading chamber 12 through the pressure sensor 64 and the processchamber 18 through the pressure sensor 68. The control module 60 thenequalizes the pressure in the two chambers 12 and 18 by adjusting thevariable restriction control valves 52 and 56 accordingly so thepressure in the loading chamber 12 10 matches that of the processchamber 18. Every time that the slit valve 22 is open between thechambers, and after the pressure of the two chamber has equalized, thecontrol module 60 calibrates the pressure sensors 64 and 68 relative toeach other.

[0027] Referring to FIG. 3, a calibration method 100 may be performed ona sensor inside the system 10 (FIG. 1). For the sake of example, thecalibration method 100 is used after a wafer 82 is placed in the loadingchamber 12 and is ready to be transferred to the transfer chamber 16.FIG. 4 shows a magnified portion of the system 10 for discussion withthe present example.

[0028] Referring also to FIG. 4, a wafer 82 is in the loading chamber12, ready for transfer to the next chamber 16 through the slit valve 22.At step 102, it is determined if the wafer 82 is ready for transfer tothe next chamber. Since in the present example, the wafer is in theloading chamber 12, step 102 determines that the chamber has beenproperly closed and sealed. At step 104, the control module 60 equalizesthe pressure between the loading chamber 12 and the next chamber (thetransfer chamber, in the present example) 16. The control module 60 willnot open the slit valve 22 until the pressure between loading chamber 12and transfer chamber 16 is equalized. Specifically, the control module60, using readings obtained from pressure sensors 62 and 64, willequalize the pressure in the transfer chamber 16 and loading chamber 12by adjusting the variable restriction control valves 42 and 52,connected to the exhaust lines 40 and 44 respectively.

[0029] Referring now to FIGS. 3 and 5, at step 106, when the controlmodule 60 receives readings from the pressure sensors 62 and 64 thatindicate the pressures in the loading chamber 12 and transfer chamber 16are equal, execution proceeds to step 108. The control module 60 sends asignal to the slit valve 22 to open, as shown in FIG. 5. The wafer 82will then be shifted to the transfer chamber 16 through the slit valve22.

[0030] While the slit valve 22 is open for the transfer of material, ifthere is any difference in the actual pressure between the loadingchamber 12 and transfer chamber 16, it will be equalized automatically.At step 110, the control module 60 will then check the readings on thepressure sensors 62 and 64. At step 112, a determination is made as towhether the pressure sensors 62, 64 are calibrated relative to eachother. If so, then execution proceeds to step 114 where the slit valve22 is closed and processing continues on in a normal progression.

[0031] If at step 112 the pressure sensors 62, 64 read differently,execution proceeds to step 116 where the sensors are calibrated relativeto each other. In one embodiment, the pressure sensor 64 is calibratedto the pressure sensor 62. By so doing, all of the pressure sensors 64,66, 68, 70 (FIG. 1) will eventually be calibrated relative to pressuresensor 62 and thus to each other. It may be desirable, on a periodicbasis, to calibrate pressure sensor 62 to a reference measurement.However, even this calibration has been simplified because only onesensor needs to be calibrated. Execution then returns to step 110. It isunderstood, however, that the control module 60 may have certain errormodules so that the method will not continually loop to step 110 if thepressure sensors cannot be properly calibrated.

[0032] Because the pressure in the two chambers is known to be equalwhile the slit valve 22 is open, calibrating the sensors 62 and 64relative to each other eliminates the potential for a rush of processingfluid and constituents between the chambers the next time the valve isopen. Also, because the process of relative calibration is performedevery time the slit valve 22 is opened, a variation of no more than0.01-0.02 Torr should occur between any two calibrations. This is animprovement over the prior art, where variations of 5 Torr or greaterbetween chambers would be common because of the infrequency ofcalibration.

[0033] Furthermore, because the relative calibration is done duringactual use, the system does not have to be shut down to performcalibration routines quite as often as conventional systems. This, ofcourse, results in increased productivity and cycle time.

[0034] Further still, the control module 60 can maintain a history ofcalibrations to determine if any of the pressure sensors must berepeatedly calibrated. This may indicate that the particular pressuresensor or corresponding chamber is faulty. Likewise, if a majority ofthe pressure sensors must be repeatedly calibrated, this may indicatethat the pressure sensor for the transfer chamber 16, or correspondingchamber, is faulty.

[0035] Although the invention has been described with reference tospecific embodiments, such as the manufacture of integrated circuitsemiconductors, this description is not meant to be construed in alimited sense. The invention can be used in a variety of processes.Also, different types of valves and chamber may equally benefit from thepresent invention. Various modifications of the disclosed embodiments,as well as alternative embodiments of the inventions will becomeapparent to persons skilled in the art upon reference to the descriptionof the invention. It is, therefore, contemplated that the appendedclaims will cover such modifications that fall within the scope of theinvention.

What is claimed is:
 1. A method for maintaining a consistent pressurebetween two chambers in a processing facility, wherein the two chambershave a slit valve there between, the method comprising the steps of:determining when the slit valve is open; measuring a pressure of thefirst chamber while the slit valve is open; measuring a pressure of thesecond chamber while the slit valve is open; calibrating first andsecond pressure sensors, associated with the first and second chambers,respectively, relative to each other while the slit valve is open; andclosing the slit valve when the pressure sensors have been calibratedrelative to each other.
 2. The method of claim 1 wherein the slit valveis a vacuum-sealed door.
 3. The method of claim 1 wherein thecalibrating is performed by changing a reading value of the firstpressure sensor to be in accordance with the second pressure sensor. 4.The method of claim 3 wherein the second chamber is a transfer chamberconnecting the first chamber to a third chamber.
 5. The method of claim3 further comprising: monitoring the change of the reading value of thefirst sensor; and determining if the change indicates a faulty system.6. A method for maintaining a consistent pressure in a processingfacility having a transfer chamber used to transfer materials to andfrom a process chamber, wherein the two chambers have a valve therebetween, the method comprising the steps of: determining when the valveis open; measuring a pressure of the transfer chamber while the valve isopen; measuring a pressure of the processing chamber while the valve isopen; calibrating a pressure sensor on the processing chamber relativeto a pressure sensor on the transfer chamber while the valve is open;and closing the valve when the pressure sensors on the processingchamber and transfer chamber are relatively calibrated.
 7. The method ofclaim 6 wherein the transfer chamber is also used to transfer materialsto and from a loading chamber, the transfer chamber and loading chamberhaving a second valve there between, the method further comprising:determining when the second valve is open; measuring a pressure of thetransfer chamber while the second valve is open; measuring a pressure ofthe loading chamber while the second valve is open; calibrating apressure sensor on the loading chamber relative to the pressure sensoron the transfer chamber while the second valve is open; and closing thesecond valve when the pressure sensors on the loading chamber andtransfer chamber are relatively calibrated.
 8. An automated system forcontrolling processing of a product in a processing facility, saidsystem compromising: first, second, and third chambers; first, second,and third pressure sensors associated with the first, second, and thirdchambers, respectively, for measuring a pressure inside each chamber;first, second, and third exhaust lines connected to the first, second,and third chamber, respectively; first, second, and third pressurerestriction control valves connected to the first, second, and thirdexhaust lines, respectively; a first material transfer valve connectingthe first chamber to the second chamber; a second material transfervalve connecting the second chamber to the third chamber a controlmodule connected to the first and second material transfer valves, thefirst, second and third pressure sensors, the first, second and thirdvariable restriction control valves, and the first, second and thirdchambers, the control module including processing capabilities forperforming the steps of: measuring the pressure in the first and secondchamber while the first material transfer valve is closed; adjusting thefirst and second variable restriction control valves until the first andsecond pressure sensors have similar readings while the first materialtransfer valve is closed; and calibrating the first pressure sensor togenerate a reading similar to that of the second pressure sensor whenthe first material transfer valve is open.
 9. The system described inclaim 8 wherein the first and second material transfer valves arevacuum-sealed doors.
 10. The system described in claim 8 wherein thetransfer chamber includes a robot for handling of the materials beingprocessed.
 11. The system described in claim 8 wherein the controlmodule also includes processing capabilities for: detecting a fault inthe system by monitoring the adjustment of the first pressure sensorover a period of adjustments.
 12. The system described in claim 8wherein the control module also includes processing capabilities for:measuring the pressure in the second and third chambers while the secondmaterial transfer valve is closed; adjusting the second and thirdvariable restriction control valves until the second and third pressuresensors have similar readings while the second material transfer valveis closed; and calibrating the third pressure sensor attached to thethird chamber to generate a reading similar to that of the secondpressure sensor when the second material transfer valve is open.
 13. Thesystem described in claim 12 wherein the control module also includesprocessing capabilities for: detecting a fault in the system bymonitoring the adjustment of the first, second, and third pressuresensors over a period of adjustments.
 14. The system described in claim13 wherein the control module also includes processing capabilities for:determining that the fault is associated with the third chamber if onlythe third sensor requires significant adjustment over the period ofadjustments.
 15. The system described in claim 13 wherein the controlmodule also includes processing capabilities for: determining that thefault is associated with the second chamber if both the first and thirdsensors require significant adjustment over the period of adjustments.